1. Field of the Invention
The present invention relates to a device for detecting the position of a movable head such as tool slide, work table or the like in machine tools. More particularly, it relates to such a detection device suitable for use at those portions of machine tools which are contaminated by coolant, chips, dust or the like.
2. Description of the Prior Art
Generally, numerical control machine tools are provided with a device for detecting the position of a movable head. A typical position detection device for such purpose includes a linear scale with scale gratings secured to a machine base and a scanning unit secured to a movable head for reading the scale gratings on the linear scale upon movement of the movable head. For precise position detection, the linear scale and the scanning unit must be protected against contamination by dust, chips, coolant and the like. To this end, in a known device as disclosed in Japanese unexamined, published patent application No. 59-183307, a housing fixed to a machine tool bed accommodates therein a linear scale attached to the housing and a scanning unit connected to a movable head. However, sealing elements for covering an opening of the housing do not provide a fluidtight capability because they cannot perfectly seal opposite end portions of a connection member which extends through the opening of the housing to connect the scanning unit to the movable head.
Particularly, in grinding machines, the tilting of a wheel carrier or head occurs due to a grinding resistance, and for diminishing the affect by such tilting motion of the wheel head, it is desirable to dispose a detection device of the aforementioned type at one side of the wheel head where a grinding wheel is also disposed. However, such one side of the wheel head is subjected to splashing of coolant, and therefore, the position detection device as used in the grinding machines is required to have an enhanced fluidtight capability.